Hitherto, various cooling measures have been employed in semiconductor elements mounted on various electrical appliances such as personal computers and other devices, because if heat generated as a result of driving is accumulated, driving of the semiconductor elements and peripheral devices may be adversely affected. As a method for cooling electronic parts such as semiconductor elements, there are known, for example, a method for mounting the device with a fan to cool the air in the device housing, and a method for mounting the semiconductor element to be cooled with a heat sink such as a heat dissipation fin and a heat dissipation plate.
When a heat sink is mounted on the aforementioned semiconductor element to perform cooling, a thermal conducting sheet is provided between the semiconductor element and the heat sink in order to efficiently dissipate heat in the semiconductor element. As this thermal conducting sheet, a sheet obtained by adding a filler such as a thermal conducting filler in a dispersed state in a silicone resin is widely used. As one example of the thermal conducting filler, carbon fibers are favorably employed (for example, see PTLs 1 to 4).
However, the thermal conducting sheet containing the carbon fibers is excellent in thermal conductivity, but has a problem that electrical conductivity easily becomes high.
Therefore, for the purpose of increasing an insulating property of the thermal conducting sheet, a thermal conducting sheet including thermal conducting fibers in which an electrically insulating material is coated on the surfaces of electrically-conductive, thermally-conductive fibers has been proposed (see, PTL 5).
However, this proposed technique is insufficient because an excellent thermal conductivity and an excellent insulating property that have been demanded in recent years cannot be achieved.